That´s true. I tried to compensate the plastic reduce UV measure in the program. But not works. In anytime I want to find a permanent place to the device with the temperature-pressure sensor outside, But the UV sensor need to be protect. So I have to find a quartz crystal that the only thing that lets UV radiation pass.

Finally I used three AA rechargeable batteries to reach a voltage of 4V in order to have a good power of transmission. But if you want something rechargeable and long-lasting, use LiFePO4 .

Yes, I have use the original shipped with Arduino. Usually I do not have coverage problems. Do you have any suggestions for another type of antenna?